It is one of the basic functions of a computer system to communicate with remote peripheral devices in order that data transfers and control signals may be interchanged in order to accomplish the purposes designed into the computer system or network.
In order to facilitate this data interchange, there have been developed peripheral controllers, also called I/O controllers or Data Link Processors (DLP's), which relieve the main host computer of many of its operating cycles for the purposes of seeing to it that data exchanges between various remote peripheral devices and the main host computer system can be accomplished with minimal interruption to the main host computer system.
A series of specialized I/O controllers have been developed by the Burroughs Corporation for handling the specialized requirements of Burroughs computer systems and peripherals. These specialized peripheral controllers have been designated as "data link processors", or DLP's.
These specialized Burroughs data link processors have been specifically designed to handle the applicable protocols and the various data transfer requirements usable by Burroughs computer and Burroughs peripheral devices. Such types of data link processors have been described in such prior patents as:
U.S. Pat. No. 4,313,162 entitled "I/O Subsystem Using Data Link Processors"; U.S. Pat. No. 4,371,948 entitled "Train-Printer-Data Link Processor"; U.S. Pat. No. 4,390,964 entitled "Input/Output Subsystem Using Card Reader Peripheral Controller".
These background patents are included herein by reference to furnish the background and functional operation of data link processors which are used to link a host computer and peripheral terminals.
These patents describe the unique features and operations of the Burroughs type of data link processors and provide specific details of operation of the data link processors in conjunction with Burroughs computer systems and networks. These prior patent applications describe the various types of possible operations and data transfer control signals which are used in data link processors. Accordingly, these patent applications will provide an in depth background and explanation of the various hardware and intercooperating features which are used in data link processors.
As a matter of background, the Burroughs type of data link processors (I/O controllers, also formerly called line control processors) are designated as "status driven". This means that each condition of operation of a DLP (data link processor) is assigned a "status number" which indicates the condition of the DLP and what it is capable of doing in that condition. Thus, the host computer and also the DLP itself must keep cognizant of the "status number" of the DLP.
The "status" driven nature is shown in U.S. Pat. No. 4,390,964 at column 12 and Table O-SS. This patent is entitled "Input/Output Subsystem Using Card Reader Peripheral Controller" and is included by reference.
Another description of usage of the status count is described in U.S. Pat. No. 4,162,520 in connection with FIGS. 7A, 7B, 7C, 7D, 7E-1, 7E-2. This patent is entitled "Intelligent Input/Output Interface Control Unit for Input-Output Subsystem" and is also included by reference.
The information as to the status count condition of each one of several DLPs in a system is important data for the host computer and other control elements in the system, especially where interface logic is shared by two or more DLPs.
The present invention is a data link processor which is compatible with Burroughs computer networks and systems but which has been specifically developed to handle two types of remote peripheral devices by means of one single data link processor. This data link processor is called the buffered printer-tape data link processor (PT-DLP) and is disclosed herein.